1. Field of the Invention
The present invention relates to a photoelectric conversion apparatus and, more particularly, to a signal readout circuit.
2. Description of the Related Art
Photoelectric conversion apparatuses have been widely used in digital cameras in recent years. Typical types of photoelectric conversion apparatuses include charge coupled device (CCD)-type photoelectric conversion apparatuses and metal oxide semiconductor (MOS)-type photoelectric conversion apparatuses. A typical MOS-type photoelectric conversion apparatus includes a pixel unit with photoelectric conversion elements, such as photodiodes, a signal storage unit that stores signals supplied from the pixel unit, and common signal lines (horizontal signal lines) through which signals from the signal storage unit are externally output.
The photoelectric conversion apparatuses have increased in size and in the number of pixels, and the number of switch transistors and the length of the signal lines also have increased along with the increase in size and in the number of pixels. Accordingly, the line capacitance including the parasitic capacitance of the common signal lines have tended to increase. In addition, an increase in the speed of signal readout is required to accommodate the increase in the number of pixels. The speed of the signal readout is affected by a reset operation of the common signal lines and the line capacitance of the common signal lines. The reset of the common signal lines means that the voltages of the signal lines are set to predetermined voltages before or after signals are read out from the signal lines.
Japanese Patent Laid-Open No. 2003-224776 discloses a photoelectric conversion apparatus configured such that a signal supplied from the pixel unit is read out into a corresponding block line and, then, is supplied to a corresponding common signal line in order to reduce a line capacitance of the common signal line.
As for the reset operation of common signal lines, Japanese Patent Laid-Open No. 10-191173 discloses a configuration including a switch that connects multiple common signal lines to each other.